The invention concerns an emergency release device for the parking lock of a motor vehicle having an operation mechanism that is pressed by a spring element into its engaged position and which can be moved against the spring force into its disengaged position by at least one actuator which is actuated by a control element. The operation mechanism can be connected with a release lever situated in the driver""s cab of the vehicle or, more broadly, on an operator""s platform, by means of a mechanical connecting element, in such a way that the parking lock can be released in the case of a malfunction.
In modern motor vehicle gears (synchronized, power shift, or automatic gears), the parking lock is usually inserted manually, via a mechanical rod, so as to block the rotating movement of gears or vehicle wheels, in a positive manner. In order to improve comfort, gears are made with electrically actuated gear shifting, so that the gear shifting command is carried out by the operator by pressing a button. Logically, the parking lock should also be included in this servo control. When using infinitely variable change-speed gears, which can implement a non-positive standstill by selecting an infinitely large speed increasing ratio, the parking lock actuation should be automated, so that the transition from non-positive standstill into parking position (and vice-versa) takes place without interruption of the braking effect of the motor vehicle. Therefore, efforts are being made to design the actuation of a parking lock (of a mechanical, positive locking of a toothed wheel) so that the locking and release of the parking lock is carried out by an electrical command transmission.
Such automated operations of the parking lock function are usually carried out in such a way that when the vehicle is stopped, the parking lock is engaged via a mechanical spring. When the vehicle is started, the parking lock can be disengaged, for example, electrically or hydraulically, against the force effect of the spring by means of auxiliary energy present on board. If this auxiliary energy fails, a manual emergency release is needed, so that the vehicle can be towed.
In case the work vehicle, for example, an agricultural tractor, must be moved or towed when its electric equipment, hydraulics, or driving motor fails, the provisioning of a mechanical emergency operation for the disengaging and re-engaging of the parking lock, parallel to the electro-hydraulic operation, is known. For example, DE-A-198 34 074 mentions an automatic gear, in which a lever is provided in the passenger space, which is operatively connected with a parking catch. For the operating connection, a Bowden cable is used, by means of which the transmission of undesired vibrations from the gear to the passenger compartment is to be avoided. The known solutions for an emergency actuation of the parking lock, however, do not fulfill all safety requirements for a modern work vehicle with automatic gears, so as to avoid dangers which may arise as a result of operating errors.
The goal, which is the basis of the invention, is to be found in providing an emergency release device of the type previously mentioned, by means of which, the aforementioned problems are overcome. In particular, dangers arising from operating errors are to be avoided. The emergency release device should consist of simple, low-cost elements and make possible foolproof remote control with a driving motor which is running or standing still. It should make possible a quick, simple, and easy emergency release of the parking lock.
The emergency release device according to the invention operates with the parking lock of a motor vehicle having an operation mechanism that is pressed by the retention force of spring elements into an engaged parking lock position and is moved by at least one actuator. The actuator is operated by a control element, against the retention force, into its engaged position. The operation mechanism can be releasably connected, by means of a mechanical connecting element, with a clutch pedal located on the operator""s platform of the vehicle. The releasable connection is designed in such a manner that an operating connection can be established between the clutch pedal and the parking lock, in a simple manner, any time and anywhere, in order to effect an emergency release of the parking lock by operating the clutch pedal. A mechanical force introduction for the disengaging of the parking lock, which is parallel to the actuator, is produced by the connection of the clutch pedal with the parking lock.
The emergency release device, in accordance with the invention, can be implemented by very simple, low-cost components. An additional lever in the passenger space, as is provided by the state of the art, is not necessary. The coupling with the available clutch pedal reduces the danger of operating errors, because for emergency operation, for example, during towing, the parking lock can be released only with a disengaged coupling. Thus, with such a type of emergency operation, the drive train between the gear and the vehicle wheels is always interrupted. The emergency release can be undertaken, independently of whether the driving motor is running or standing still. In order to make the emergency release effective, one only has to affix a cab-side end of the connecting element to the clutch pedal. This can be done simply and quickly, anywhere and any time, perhaps with the aid of a simple tool. The parking lock of a vehicle that has developed a problem during operation can thus be released, so as to allow towing of the vehicle.
The emergency release via the clutch pedalxe2x80x94that is, with the power of one""s footxe2x80x94is advantageous from the aspect of the operating force, since the restoring springs of the operation mechanism of the parking lock must be designed especially powerful to attain a high engaging speed. These forces can easily be applied and overcome with a foot.
Advantageously, the connecting elements contain a Bowden cable, one of whose ends is affixed, directly or with the insertion of other components, to the operation mechanism. The Bowden cable is conducted to the driver""s cab. Its other end is kept in the vicinity of the clutch pedal during normal operation and is not connected to the clutch pedal, so that the emergency release is not functioning.
If the emergency release is needed, for example, for the towing of a defective vehicle, the cab-side end of the Bowden cable can be connected, directly or with the insertion of other components, to the clutch pedal with a few simple moves (if necessary, with the aid of a tool). Upon connecting, the clutch pedal is at rest, which corresponds to an engaged coupling. During this installation work, the vehicle assumes a safe parking position.
To release the parking lock, the clutch pedal must then be merely depressed. The operator has to be in the driver""s seat. Therefore, he has the vehicle under control at the moment the parking lock is disengaged and can, at any moment, engage the parking lock, once again, via the clutch pedal, and can also operate the lock and the steering in the usual manner. The emergency release device can be readily placed out of commission once again, in that the cab-side end of the Bowden cable is easily detached from the clutch pedal.
Basically, the connecting elements, for example, the Bowden cable, can be affixed to any arbitrary part of the operation mechanism for the parking lock. They can act, for example, on a mechanical locking rod, through which a lock handle of the parking lock is actuated.
Frequently, the parking lock, as an actuator, contains a hydraulic cylinder, whose operating piston acts on a locking rod, which is pressed into the locked position by a spring element, and presses it into the released position when the operating piston acts against the retention force of the spring element. The operating piston can be regarded as part of the operation mechanism, on which the connecting elements act in a particularly advantageous refinement of the invention. By means of this measure, the normal operation of the parking lock is not hindered, since if the emergency release is not actuated, the parking locking device reacts as usual. The operating piston is pressed against a first stop, which corresponds to the locked position, by the spring force. If the piston chamber is set under pressure, then the operating piston is pressed against a second stop, which corresponds to the released position, and the locking rod disengages the parking lock. These normal movements of the parking lock device do not lead to a movement of the emergency actuation. On the other hand, the emergency actuation can be kept permanently in the locked actuation position under the effect of force.
Advantageously, an axially movable actuation element, for example, an actuation bolt, extends through a wall of the hydraulic cylinder and is sealed off with respect to the wall. In an actuation of the actuation element, it acts on the operating piston, and moves it into its release position against the force of the spring element. This development is particularly advantageous if the locking rod of the parking lock is located within a gear housing and is thus accessible only with difficulty, whereas the hydraulic cylinder is affixed outside on the gear housing and allows easy access. The aforementioned development reduces the construction expense and facilitates later upgrading.
A simple development of the invention is given in that the actuation element projects into the piston chamber of the hydraulic cylinder and acts on the front side of the piston. Moreover, it is advantageous to provide a shift lever, whose middle area pivots on a housing part, for example, on the gear housing. One end of the Bowden cable acts on the first end of the shift lever, whereas the second end of the shift lever acts on the actuation element, so as to move it axially if necessary.
In order not to have to constantly operate the clutch pedal during a towing operation over a long stretch, locking elements are provided in accordance with a preferred refinement of the invention; by means of these locking elements, the clutch pedal can be locked in its depressed position (parking lock released). A bolt, which is stuck into the carrier of the clutch pedal by the operator, can, for example, be taken into consideration as a locking element. This locking can thus be operated by the operator, when he is on the operator""s platform and keeps the clutch pedal depressedxe2x80x94that is, has the vehicle under control here also.
If the aforementioned locking is not used, but rather the towing operation is carried out with a depressed pedal and if the operator allows the clutch pedal to be partially engaged during the trip, due to carelessness, then there is no danger of a sudden blocking of the drive wheels, since the lock handle is turned down to low speeds of the turning toothed wheel. Moreover, the operator is warned already, in the case of the slightest contact of the tooth tips, by a loud noise and can react appropriately.
A preferred refinement of the invention provides for at least the use of a coupling sensor, which detects the position of the clutch pedal. As a coupling sensor, one can take into consideration, in particular, a position switch, which switches when the clutch pedal is depressed. In any case, coupling sensors are available, for the most part, especially with vehicles with automatic gears, and can be used for the purposes of the invention. For this reason, a special sensory mechanism is frequently not required. If the clutch pedal is depressed, the coupling sensor emits a corresponding signal to the gear control, which causes the coupling to be opened or to remain open. Thus, it is ensured, even for a towing operation with an emergency-released parking lock, that the gear remains separated from the vehicle wheels.
In the case of a vehicle with automatic gears, signal emitters, such as potentiometers and switches, on the clutch pedal emit control signals to the electronic gear control in order to place the gears on xe2x80x9cneutralxe2x80x9d or xe2x80x9cfree-wheel,xe2x80x9d as soon as the clutch pedal is depressed. These control signals are also produced when the clutch pedal is actuated for towing, in an emergency actuation, for example, upon loss of the parking lock function. The driving motor of the vehicle may be operating, in order to make available the supply pressure for the power steering and the power lock. Therefore, no other response sensors, which communicate to the gear control that the parking lock was manually disengaged, are needed for the emergency release of the parking lock. Improper use, via the link between the emergency release and the clutch pedal, in which the vehicle is operated with a permanently released parking lock, is not possible. Since no additional sensors are required, sensors cannot be additional potential sources of mistakes either.
The emergency release, in accordance with the invention, is robust and safe even if, in spite of the normal functioning of the electro-hydraulic actuation, the emergency release is used by mistake. The use of a Bowden cable makes possible any remote actuation. The emergency release is foolproof, since its operation rules out the normal operation of the vehicle. It can be used with the driving motor, both when it is running and when it is standing still.